In general, the present invention relates to temperature, stress, and chemical telemetry using sensing elements remotely located from associated electromagnetic (EM) emission pick-up and processing units that, in operation, detect emissions from the element. The invention targets temperature sensing, sensing and characterization of localized stress conditions of a solid analyte, and the monitoring one or more corrosive. More particularly, the invention is directed to a novel telemetering apparatus that employs a receiver to measure the intensity of electromagnetic emissions from a magnetically soft sensor element, whereby there is no hardwire connection between the receiver and the sensing element, and the receiver xe2x80x98listensxe2x80x99 for harmonics of the fundamental resonant frequency in order to carry out the temperature, stress, and corrosive monitoring telemetry. The invention is further directed to new telemetry techniques associated with the sensing apparatus of the invention, including: sensing temperature, determining stress conditions of a solid undergoing analysis, and sensing the presence or absence of, type, concentration of, or degradation caused over time by, one or more corrosive (such as chlorine) in a wide variety of environments. For example, the new apparatus provides a way to measure temperature, stress conditions, and corrosives, including: (a) sensing material degradation or localized permanent deformation (of single materials, composites, or laminates) caused by corrosion, temperature fluctuation, weather conditions, etc., thus, allowing for the identification of regions of actual or potential material fatigue and failure; (b) sensing internal or surface stress due to applied loads such as are experienced by construction materials (building or roadway), including repeated or prolonged exposure to a load, explosion, wind and weather conditions; (c) sensing temperature or corrosive concentration and/or type within a test sample or product packaging (during quality inspections/audit); and so on.
The new sensing element structures and technique provide information about a solid analyte or an environment utilizing the harmonic response of EM emissions of one or more sensor structures made of a magnetically soft sensing element. Furthermore, a magnetically hard (MH) element supporting a biasing field adjacent the magnetically soft sensing element can be included to provide additional functionalities, including: EM background noise; element ON-OFF switch; and biasing field response, where needed, by selective response of the MH element upon exposure to chemical species.
General Technical Background Discussionxe2x80x94Other Telemetry Devices
As is generally well known, electric and magnetic fields are fundamentally fields of force that originate from electric charges. Whether a force field may be termed electric, magnetic, or electromagnetic hinges on the motional state of the electric charges relative to the point at which field observations are made. Electric charges at rest relative to an observation point give rise to an electrostatic (time-independent) field there. The relative motion of the charges provides an additional force field called magnetic. That added field is magnetostatic if the charges are moving at constant to velocities relative to the observation point. Accelerated motions, on the other hand, produce both time-varying electric and magnetic fields termed electromagnetic fields. For general reference see the textbook, Engineering Electromagnetic Fields and Waves, Carl T. A. Johnk, John Wiley and Sons, 2nd Edition (1988).
Anti-theft markers/tags (electronic article surveillance, EAS, markers) generally operate by xe2x80x9clisteningxe2x80x9d for acoustic energy emitted in response to an interrogating AC magnetic field, to sense the presence of an EAS marker. Sensormatic, Inc. distributes an EAS tag (dimensions 3.8 cmxc3x971.25 cmxc3x970.04 mm) designed to operate at a fixed frequency of 58 kHz (well beyond the audible range of human hearing). These EAS tags are embedded/incorporated into articles for retail sale. Upon exiting a store, a customer walks through a pair of field coils emitting a 58 kHz magnetic field. If a tag is still in an article being carried by the customer, the tag will likewise emit a 58 kHz electromagnetic signal that can be detected using a pickup coil, which in turn may set off an audible or visual alarm. More-recently, these tags are being placed in a box-resonator, sized slightly larger than the tag, such as the tags placed within a cavity 20 of a housing (see FIG. 2 of Winkler et al.).
Winkler et al. describes an electronic article surveillance (EAS) anti-theft system that operates by detecting mechanical resonances of magnetostrictive elements made of amorphous metallic glass METGLAS(copyright) 2826 MB, to prevent or deter theft of merchandise from retail establishments. In response to an interrogation signal generated by energizing circuit 201, the interrogating coil 206 generates an interrogating magnetic field, which in turn excites the integrated marker portion 12 of the article of merchandise 10 into mechanical resonance. During the period that the circuit 202 is activated, and if an active marker is present in the interrogating magnetic field, such marker will generate in the receiver coil 207 a signal at the frequency of mechanical resonance of the marker. This signal is sensed by a receiver which responds to the sensed signal by generating a signal to an indicator to generate an alarm.
Anderson, III et al. discloses a marker 16 (FIG. 5) formed of a strip 18 of a magnetostrictive, ferromagnetic material adapted, when armed in its activated mode, to resonate mechanically at a frequency within the range of the incident magnetic field. A hard ferromagnetic element 44 disposed adjacent to the strip 18 is adapted, upon being magnetized, to magnetically bias the strip 18 and thereby arm it to resonate at that frequency. An oscillator provides an AC magnetic field within interrogation zone 12 to mechanically resonate a magnetostrictive strip 18, which has first been armed by a magnetized hard ferromagnetic element 44, upon exposure to this AC magnetic field. The sole object of Anderson, III et al. EAS marker is to detect the presence between coil units 22 and 24 (interrogation zone 12) of an xe2x80x9carmed/activatedxe2x80x9d marker 16. In the event an activated marker 16 secured to a retail article is detected within zone 12, an alarm will sound. A deactivator system 38, electrically connected to a cash register, can be used to deactivate the marker.
Humphrey and, another reference, Humphrey et al. disclose a type of electronic article surveillance (EAS) marker which includes a thin strip or wire of magnetic material that, when exposed to an alternating interrogation signal of low frequency and low field strength, responds by generating a signal pulse that they state xe2x80x9ccauses a regenerative reversal of magnetic polarity generating a harmonically rich pulse that is readily detected and easily distinguished.xe2x80x9d And while the Humphrey references recognize that high harmonics are detectable for the low frequency interrogation fields they use, once again, it is simply the presence or absence of the EAS marker that is of any interest.
Schrott, et al. describes a multibit bimorph magnetic ID tag for attachment to, and identification of, an object. The tag has one or more bimorphs comprised of a thin strip of a magnetostrictive material attached to a thicker bar 21 of hard magnetic material. A shipping pallet, package, or product is tagged with the bimorph for later product identification. Schrott et al. indicates that a multibit tag could be programmed to generate a binary or other suitable code. In the binary code case, a certain frequency of an array of cantilevers can be assigned a value of xe2x80x9czeroxe2x80x9d or xe2x80x9conexe2x80x9d and, if absent, it can take the opposite value. The Schrott, et al. ID tag is limited to coded (zeros and ones) identification of the object. If, in operation, a Schrott, et al. ID tag""s resonant frequency (predetermined by size/materials) is not xe2x80x9chitxe2x80x9d during interrogation due to some unexpected event/external factor (such as, its resonant frequency is changed due to a temperature swing, or due to reaction of the ID tag with a surrounding fluid), no response will be detected and an incorrect output code will result, thus, destroying the Schrott, et al. ID tag""s function.
Rather than working at a fixed interrogation frequency and simply checking for amplitude like the anti-theft EAS markers do to sense presence or absence of an active EAS tag or marker on an article for purchase exposed to an interrogation field, the novel sensing apparatus and associated technique of the invention looks to the harmonic frequency response of a magnetically soft sensor element for information about temperature, stress conditions of a solid analyte, or a corrosive of interest. Operating as a telemeter, EM emissions are obtained through remote query according to the invention, without direct hard-wire connection and without the need to ensure the sensor element""s orientation in order to provide such information. In effect, the high-frequency and low frequency time-varying interrogation fields to which the sensor element is exposed effectively empowers the xe2x80x98passivexe2x80x99 sensing element(s) of the invention, allowing for harmonic amplitude values of EM emissions to be identified.
It is a primary object of this invention to provide a telemetering apparatus for gathering information about temperature, stress conditions of a solid analyte, and corrosives within an environment or analyte, utilizing the harmonic frequency response of EM emissions from a magnetically soft sensing element upon concurrent exposure to high-frequency and low frequency interrogation fields. A receiver, remote from the magnetically soft element, is engaged to measure the intensity of EM emissions to identify a corresponding harmonic amplitude value, or series of values. A unit, such as a processor of suitable type, a computerized device having processing capability, and so on, is employed to determine a value for temperature, stress conditions, or corrosion (i.e., the value of interest) using the harmonic frequency amplitude value identified.
Advantages of providing the new sensing apparatus and associated technique, include without limitation:
(a) Mode of operationxe2x80x94The invention can be used for one-time disposable operation (e.g., in the form of a kit, whereby the sensor element is embedded within a solid analye or initially placed within packaging) or for continuous monitoring.
(b) Versatility of usexe2x80x94The apparatus may be used for individual measurements or on-going monitoring of temperature fluctuations, stress conditions, or a corrosive to allow for observation of characteristics of a solid analye (whether a single material or a composite or laminate) such as concrete, mortar, tar, wood, fiberboard, particleboard, plasterboard, sheetrock, fiberglass, plexiglass, resins, and plastics (including thermoplastics, and thermoformable, and thermoset plastics), as the analyte reacts to some agent, load, or other event over time, such as observing material degradation or deformation due to corrosion, exposure to a single catastrophic event (e.g., explosion or earthquake), repeated loads such as wind or auto travel (in the case of tarmac on roadways), weather conditions, and so on, thus, allowing for identification of material fatigue or failure in a nondestructive manner.
(c) Simplicity of use/Speed of resultsxe2x80x94The new sensing apparatus can produce measurement results, real-time, on-site with relative ease. The monitoring technique may be used alone or coupled with other current analysis methods such as visual inspection (in the case of buildings, fiberglass components of aircraft, roadways). Sensing data may be gathered within a few milli-seconds, or so.
(d) Apparatus design simplicityxe2x80x94Reducing the number and size of components required to accomplish measurements/monitoring reduces overall fabrication costs, making manufacturing economically feasible, and adds to ease of operation.
(e) Versatility of designxe2x80x94The sensor elements can be formed into many different shapes of various sizes; for example, the sensor elements may be fabricated on a small scale (a few millimeters) for use where space is extremely limited such as within small-sized sealed packaging or where embedded within a material, or on a larger scale (several centimeters). Several sensor elements may be incorporated or grouped into an array to provide a xe2x80x98packagexe2x80x99 of various desired information or multiple parameters by sampling or measuring EM emission simultaneously or sequentially. This enables several measurements to be made with sensor element structures in an otherwise complex environment (e.g., a temperature measurement may be taken along with measurements relating to the concentration/presence/absence of a corrosive).
Briefly described, once again, the invention includes a temperature sensing apparatus that includes a sensor element made of a magnetically soft material operatively arranged within a first and second time-varying interrogation magnetic field, the first time-varying magnetic field being generated at a frequency higher than that for the second magnetic field. Preferably, the second, lower frequency interrogation field is quasi-static, i.e., effectively operating as a dc (direct current) biasing field, selected to maximize the harmonic emission amplitudes measured from the sensor element in response to the higher frequency, first interrogation field.
A receiver, remote from the sensor element, is engaged to measure intensity of electromagnetic emissions from the sensor element to identify a relative maximum amplitude value for each of a plurality of higher-order harmonic frequency amplitudes so measured. A unit (comprising a processor, or other data processing device) is employed to determine a value for temperature using the relative maximum harmonic amplitude values identified. In another aspect of the invention, the focus is on an apparatus and technique for measurement EM emission intensity from a magnetically soft sensor element to determine a value for of stress condition of a solid analyte using the relative maximum harmonic amplitude values identified. In a third aspect of the invention, the focus is on an apparatus and technique for measurement of EM emission intensity from a magnetically soft sensor element to determine a value for corrosion using the relative maximum harmonic amplitude values identified.
There are many further distinguishing features of the apparatus and technique of the invention. The receiver can comprise an electromagnetic pick-up coil and associated EM emission detection circuitry such as a spectrum analyzer. The sensor element-maybe located within a solid analyte a component of which is a material selected from the group consisting of concrete, mortar, tar, wood, fiberboard, particleboard, plasterboard, sheetrock, fiberglass, plexiglass, resins, and plastics. The sensor element may be embedded within, located on a surface of, interposed between layers of, etc., the solid analyte so that, in operation, it can collect localized sensing information about the solid. The sensor element may be elongated in shape, having a length, e, from 1 mm to 1000 mm, and may be at least partially encapsulated within a corrosion-resistant casing if operated within an environment where reaction to an agent produces undesirable affects. A magnetically hard (MH) element supporting a biasing field adjacent the magnetically soft sensor element can be included. For example, the MH element may be made of a material chemically responsive to a fluid analyte such that exposure thereto causes a change in the biasing field.
The higher frequency of the first field may be selected from a first range of frequencies (50 Hz to 10 MHz) and the frequency of the second field may be selected from a second range of frequencies (0.1 Hz to 10 Hz). The second field of lower frequency is of an amplitude selected to correspond to offset that of a MH element""s stray field, in the event a MH element is incorporated with the apparatus. The first, higher frequency interrogation field may be generated continuously over time (e.g., steady state over a selected time interval) or generated in the form of a pulse, or signal-burst of, for example, approximately 20 cycles generated at the higher frequency, during which time the measurement of EM emission intensity is made. Preferably the second, lower frequency interrogation field is generated continuously over the time period during which the high frequency field is generated so that EM emission intensity measurements can be taken to identify harmonic frequency amplitude values. It is the first, higher frequency field produced in conjunction with the quasi-static second time-varying field that provides a mechanism by which relative maximum amplitudes for the harmonic(s) of interest can be identified, thus, allowing for a value for the parameter of interest (temperature, stress conditions, corrosion) to be determined. By sweeping the second, quasi-static interrogation field amplitude, a relative maximum of the harmonic EM emissions of interest from the sensor element can be identified-this amounts to a xe2x80x98trackingxe2x80x99 of relative changes in EM emission intensity between several different higher-order harmonics to provide the parameter value (temperature, stress, corrosion) of interest.
The first and second interrogation fields may be transmitted by a single interrogation field generating coil or separate coils; one may choose to use a single coil to not only generate the first and second interrogation fields but also aid in the detection of EM emissions from the sensor element by operating as part (pick-up coil) of the receiver. Preferably the emissions measured and relative maximum harmonic frequency amplitude values identified are for higher-order harmonics ranging from, preferably, the 2nd to 100th harmonic of the fundamental resonant frequency for the sensor element.
A pre-correlation made between a series of comparative relative maximum harmonic amplitude values and a corresponding series of temperature, stress conditions, or corrosion values can be used to aid in calculation of the particular parameter value of interest. This pre-correlation can be earlier obtained using a calibration sensor element of like size and material characteristics of the sensor element used on-site, whereby the relative maximum higher-order harmonic frequency amplitudes identified, represented by a plurality of voltages corresponding to EM harmonic emission measurements, are collected and plotted against parameter values (e.g., temperature, stress, or corrosion) of interest. To automate on-going monitoring of a parameter, a computerized device To may be employed for instructing the receiver to take, over a time interval, a series of sensor element emission measurements, and communicate (or store for later use) each of a series of corresponding parameter values for these emission measurements taken. Further, a series of sensor element emission measurements may be taken over a selected response-time interval to produce a parameter response profile comprising a series of corresponding parameter values for the particular solid analyte.
The magnetically soft element is preferably made of a ferromagnetic alloy, including elements such as iron, cobalt, samarium, yttrium, gadolinium, terbium, or dysprosium. The element may take on a wide variety of shapes, including elongated ribbon shapes, rectangular-elongated, oval, elongated polygonal, etc., so long as the sensor element remains effectively magnetically soft thereby supporting a high magnetic permeability, allowing sufficient EM emission and remote receipt thereof according to the invention. For example, a width, w, that is less than three times a length, e, of the sensor element may be chosen.